1. Field of the Invention
The present invention relates to a novel high pressure phase spinel type sialon and a method for producing its powder. The present invention also relates to a novel high pressure phase spinel-type silicon oxynitride and a method for producing its powder, particularly a method for producing a spinel type silicon oxynitride by a so-called high pressure synthesis to convert a low pressure silicon oxynitride to a cubic spinel type silicon oxynitride by means of conventional various compression methods.
2. Discussion of Background
Heretofore, a synthesis of a spinel-type silicon nitride Si6N8 of the chemical formula Si6xe2x88x92xAlxOxN8xe2x88x92x where x=0, has been known. However, the presence or synthesis of a high pressure phase spinel type sialon has not been known. Likewise, the presence or synthesis of a spinel type silicon oxynitride has not heretofore been known.
A method of synthesizing a spinel type silicon nitride by reacting Si and N2 fluid in a diamond anvil cell, or by heating a low pressure phase silicon nitride (such as xcex1-Si3N4, xcex2-Si3N4 or amorphous Si3N4) under a pressure of 15 GPa at a temperature of at least 2,000 K, or by subjecting a low pressure phase silicon nitride to impulse treatment at a pressure of at least 20 GPa, is known.
It is an object of the present invention to provide a novel spinel type sialon by means of an impulse pressuring technique employing an impulse wave. If a spinel type sialon can be synthesized in a large amount, its physical properties, etc. can be investigated, and it will be possible to develop new substances, particularly new materials having e.g. an oxide such as Al2O3 or a nitride such as AlN solid-solubilized in the spinel type silicon nitride.
It is another object of the present invention to provide a novel substance of a spinel silicon nitride type by means of a conventional impulse treating technique by means of an impulse wave.
The present inventors have conducted an extensive study to accomplish the above objects. As a result, it has been found that if a proper amount of copper powder is mixed with a low pressure phase sialon powder, the mixture is press-molded to a proper density, and the molded product is subjected to impulse compression at a proper temperature and pressure for a short time of at least a certain degree, it is possible to convert it to a high pressure phase spinel type sialon powder by a single impulse treatment without changing the composition of the starting material sialon powder. Further, it has been found that if a proper amount of a copper powder is mixed to a low pressure phase silicon oxynitride powder, the mixture is press-molded to a proper density, and the molded product is subjected to impulse compression at a proper temperature and pressure for a short time of at least a certain degree, it is possible to convert it to a high pressure phase spinel type silicon oxynitride powder by solid-solubilizing an oxide SiO2 in spinel silicon nitride, without changing the composition of the starting material silicon oxynitride powder.
Thus, the present invention provides a high pressure phase spinel type sialon represented by the chemical formula Si6xe2x88x92xAlxOxN8xe2x88x92x (0 less than xxe2x89xa64.2).
Further, the present invention provides a method for producing a spinel type sialon powder, which comprises instantaneously compressing a press-molded product made of a mixture comprising a copper powder and a powder of a low pressure phase xcex2-sialon represented by the chemical formula Si6xe2x88x92xAlxOxN8xe2x88x92x (0 less than xxe2x89xa64.2), under a pressure of at least 15 GPa by an impulse wave for a pressing time of at most 5 microseconds, to let the low pressure phase xcex2-sialon undergo phase transition to a high pressure phase spinel type sialon.
The high pressure phase spinel type sialon of the present invention is capable of taking in various cations by the spinel structure and is excellent in the thermal stability or the stability in an oxidizing atmosphere. Such stability is reflected to optical or electrical nature by an addition of a trace amount of other chemical components, and it is expected to be useful not only as a mechanical material but also as an optical material or an electronic material.
The present invention also provides a high pressure phase spinel type silicon oxynitride represented by the chemical formula Si3+xO2xN4 (xe2x95x90Si3N4.xSiO2, 0 less than x less than 1).
Still further, the present invention provides a method for producing a powder of a spinel type silicon oxynitride, which comprises compressing a low pressure crystal phase powder or amorphous silicon oxynitride (compositional formula Si3+xO2xN4, 0 less than x less than 1) by an impulse wave to prepare a high pressure phase spinel type silicon oxynitride, wherein instantaneous pressing under a pressure of at least 20 GPa by an impulse wave for a pressing time of at most 5 microseconds, is applied to a press-molded product made of a mixture comprising a copper powder and a low pressure silicon oxynitride powder.
The high pressure phase spinel type silicon oxynitride of the present invention is highly dense and excellent in stability in an oxidizing atmosphere. Further, if oxygen enters the spinel structure, it takes a structure of lattice defect and shows a unique nature in its electrical characteristics, and thus, it is expected to be useful not only as a structural material but also as an electronic material.